Re: [PATCH v7 2/8] PCI: Add new array for keeping track of ordering of reset methods

[Amey Narkhede]

On 21/06/21 10:02AM, Shanker R Donthineni wrote:
> Hi Bjorn,
>
> On 6/18/21 12:22 PM, Amey Narkhede wrote:
> > I wonder if this would be easier if dev->reset_methods[] contained
> > indices into pci_reset_fn_methods[], highest priority first, with the
> > priority being determined when dev->reset_methods[] is updated.  For
> > example:
> >
> >   const struct pci_reset_fn_method pci_reset_fn_methods[] = {
> >     { },                                                     # 0
> >     { &pci_dev_specific_reset, .name = "device_specific" },  # 1
> >     { &pci_dev_acpi_reset, .name = "acpi" },                 # 2
> >     { &pcie_reset_flr, .name = "flr" },                      # 3
> >     { &pci_af_flr, .name = "af_flr" },                       # 4
> >     { &pci_pm_reset, .name = "pm" },                         # 5
> >     { &pci_reset_bus_function, .name = "bus" },              # 6
> >   };
> >
> >   dev->reset_methods[] = [1, 2, 3, 4, 5, 6]
> >     means all reset methods are supported, in the default priority
> >     order
> >
> >   dev->reset_methods[] = [1, 0, 0, 0, 0, 0]
> >     means only pci_dev_specific_reset is supported
> >
> >   dev->reset_methods[] = [3, 5, 0, 0, 0, 0]
> >     means pcie_reset_flr and pci_pm_reset are supported, in that
> >     priority order
> What about keeping two bitmap fields 'resets_supported' and 'resets_enabled' in
> pci_dev object and mange it through sysfs and probe helper function. We can avoid
> two loops multiple paces and takes only 2Bytes of memory to keep track resets.
>
> resets_supported  ---> initialized during pci_dev setup
> resets_enabled ---> Exposed to userspace through sysfs by default set to resets_supported
>
> include/linux/pci.h:
> ------------------------
> /* Different types of PCI resets possible, lower number is higher priority */
> #define PCI_RESET_METHOD_DEVSPEC     0
> #define PCI_RESET_METHOD_ACPI            1
> #define PCI_RESET_METHOD_FLR              2
> #define PCI_RESET_METHOD_Af_FLR         3
> #define PCI_RESET_METHOD_PM               4
> #define PCI_RESET_METHOD_BUS             5
> #define PCI_RESET_METHOD_MAX            6
>
> struct pci_dev {
>     ...
>         u8              resets_supported;
>         u8              resets_enabled;
> };
>
> static inline bool pci_reset_supported(struct pci_dev *dev)
> {
>         return !!(dev->resets_supported);
> }
>
>
> drivers/pci/pci.c:
> --------------------
> const struct pci_reset_fn_method pci_reset_fn_methods[PCI_RESET_METHOD_MAX] = {
>         [PCI_RESET_METHOD_DEVSPEC] = { &pci_dev_specific_reset,
>                                                                    .name = "device_specific" },
>         [PCI_RESET_METHOD_ACPI] = { &pci_dev_acpi_reset, .name = "acpi" },
>         [PCI_RESET_METHOD_FLR] = { &pcie_reset_flr, .name = "flr" },
>         [PCI_RESET_METHOD_Af_FLR] = { &pci_af_flr, .name = "af_flr" },
>         [PCI_RESET_METHOD_PM] = { &pci_pm_reset, .name = "pm" },
>         [PCI_RESET_METHOD_BUS] = { &pci_reset_bus_function, .name = "bus" }
> };
>
>
> void pci_init_reset_methods(struct pci_dev *dev)
> {
>         int i, rc;
>
>         BUILD_BUG_ON(ARRAY_SIZE(pci_reset_fn_methods) != PCI_RESET_METHOD_MAX);
>         might_sleep();
>
>         for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
>                 rc = pci_reset_fn_methods[i].reset_fn(dev, PCI_RESET_PROBE);
>                 if (!rc)
>                         dev->resets_supported |= BIT(i);
>                 else if (rc != -ENOTTY)
>                         break;
>         }
>         dev->resets_enabled = dev->resets_supported;
> }
>
> int __pci_reset_function_locked(struct pci_dev *dev)
> {
>         int i, rc = -ENOTTY;
>
>         might_sleep();
>
>         for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
>                 if (dev->resets_enabled & BIT(i)) {
>                         rc = pci_reset_fn_methods[i].reset_fn(dev, 0);
>                         if (rc != -ENOTTY)
>                                 return rc;
>                 }
>         }
>
>         if (rc == -ENOTTY)
>                 pci_warn(dev, "No reset happened reason %s\n",
>                          !!dev->resets_supported ?
>                          "disabled by user" : "not supported");
>
>         return rc;
> }
>
> drivers/pci/pci-sysfs.c
> ----------------------------
> static ssize_t reset_method_store(struct device *dev,
>                                   struct device_attribute *attr,
>                                   const char *buf, size_t count)
> {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         u8 resets_enabled = 0;
> ...
>         if (sysfs_streq(options, "default")) {
>                 pdev->resets_enabled = pdev->resets_supported;
>                 goto set_reset_methods;
>         }
>
>         while ((name = strsep(&options, ",")) != NULL) {
>                 if (sysfs_streq(name, ""))
>                         continue;
>                 name = strim(name);
>
>                 for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
>                         if ((pdev->resets_supported & BIT(i)) &&
>                             sysfs_streq(name, pci_reset_fn_methods[i].name)) {
>                                 resets_enabled |= BIT(i);
>                                 break;
>                         }
>                 }
> ...
>         }
>
> set_reset_methods:
>         kfree(options);
>         pdev->resets_enabled =  resets_enabled;
>         return count;
> }
>
> static ssize_t reset_method_show(struct device *dev,
>                                  struct device_attribute *attr,
>                                  char *buf)
> {
>         struct pci_dev *pdev = to_pci_dev(dev);
>         ssize_t len = 0;
>         int i;
>
>         for (i = 0; i < PCI_RESET_METHOD_MAX; i++) {
>                 if (pdev->resets_enabled & BIT(i))
>                         len += sysfs_emit_at(buf, len, "%s%s",
>                                              len ? "," : "",
>                                              pci_reset_fn_methods[i].name);
>         }
>         len += sysfs_emit_at(buf, len, len ? "\n" : "");
>
>         return len;
> }
>
Thank you for the idea.
Actually that would be coming full circle because Alex, Raphael and I
tried similar approach earlier while prototyping for v2 but this implementation
does look better than what I had at that time.

Thanks,
Amey